1. Field of the Invention
The invention in general relates to acoustic imaging systems for underwater use, and particularly to such systems which eliminate the requirement for an acoustic lens.
2. Description of the Prior Art
In underwater imaging systems for viewing target areas, a variety of methods exist for beam forming or image formation utilizing an array of acoustic transducers. One of the simplest methods incorporates an acoustic lens; however, at relatively low frequencies these lenses are generally too bulky to be practical.
One type of imaging system which eliminates the necessity for an acoustic lens employs a digital computer. With such a system, an image is formed from an array of acoustic transducer receiving elements providing output signals to a computer which stores the phase and amplitude received by each array element and performs a mathematical operation on the values to obtain the source distribution of the target area, which is then displayed. Such a system, however, is relatively expensive in the requirements of a digital computer and programming thereof with the computation time being relatively expensive.
Another system incorporating an array of receiving transducers sonifies an underwater target area of interest to produce a sonic image which is combined with a reference signal to generate a holographic video signal which is displayed on the face of a special tube. The special tube is illuminated with a laser beam and the hologram is converted to an object image which is picked up by a TV camera and displayed on a monitor. Although such a system eliminates the requirement for a digital computer, the "special tube" is extremely expensive and requires high voltage power supplies.